1. Field of the Invention
The present invention relates to image forming apparatus and process cartridges for such image forming apparatus.
2. Description of the Related Art
Image forming apparatuses such as copiers, printers and facsimile machines are widely used in offices. For effectively utilizing the space of such an office and for the sake of convenience, these image forming apparatuses are often placed not in a dedicated room but in the office in the vicinity of users. In the latter case, some users feel the noise from the image forming apparatus unpleasant. Sounds caused by sheet feeding or rotation of motors upon image formation in the image forming apparatus are trivial as noise, unless they are excessively loud. In contrast, noise occurring after image formation and immediately before the photoconductor stops has a frequency of 400 Hz to 1500 Hz, which is significantly lower than those of sounds occurring upon the operation of the image forming apparatus. Thus, some users may misunderstand that the image forming apparatus produces trouble. The noise has a sound level lower than those of sounds occurring during the sheet feeding and rotation of motors, but the users often feel this noise relatively loud, because it occurs after the sounds caused by image formation reduce.
The noise produced after image formation and immediately before the photoconductor comes to a stop is caused by friction between the photoconductor and a cleaning blade. When the photoconductor rotates at a low rate immediately before stop, the friction between the photoconductor and the cleaning blade increases and the increased friction causes vibration of the cleaning blade. The vibration, in turn, causes vibration of a metallic holder or sheet metal holding the cleaning blade to thereby make the noise
The cleaning blade typically made of urethane rubber becomes contorted by the action of friction with the photoconductor. At the time when the stress in the cleaning blade becomes larger than the friction force with the photoconductor, the cleaning blade rapidly returns to its original state by the action of restoring force and cleaning blade and releases the stress caused by the strain. When the cleaning blade returns to its original state, significantly large, uneven and irregular friction occurs between the cleaning blade and the photoconductor. Thus, a fluttering or chattering sound occurs in the image forming apparatus.
When the cleaning blade held by a metallic holder becomes distorted by the increased friction with the photoconductor, the metallic holder holding the cleaning blade also bends. The restoring force caused by the stress in the metallic holder adds to the restoring force of the cleaning blade upon the restoring of the cleaning blade. Thus, the friction force and friction space (length) between the cleaning blade and the photoconductor increase, and the chattering sound in the image forming apparatus becomes very loud.
The noise is trivial immediately after power-on of the image forming apparatus. However, after repetitive image formation, the temperature in the image forming apparatus elevates, and the cleaning blade becomes soft. Thus, the amplitude of the vibration of the cleaning blade increases, and the noise increases.
Certain cleaning members have the function of preventing the noise occurring upon the use of such image forming apparatuses. For example, a cleaning member comprises a metallic holder 20 having an L-shaped profile and holding a cleaning blade 17 (FIG. 1). The cleaning member has one bent portion 23. Thus, the metallic holder 20 is resistant to deformation and exhibits less distortion. The cleaning member comprising the metallic holder 20 having an L-shaped profile and the cleaning blade 17 is arranged in an image forming apparatus as shown in FIG. 2 so that the cleaning blade 17 is in contact with a photoconductor 11. The use of the cleaning member somewhat reduces the noise caused by the friction between the photoconductor 11 and the cleaning blade 17.
Japanese Patent Application Laid-Open (JP-A) No. 05-341701 (paragraphs [0004] to [0009]) discloses an image forming apparatus having a cleaning member comprising a cleaning blade for cleaning a photoconductive drum, and a vibration absorption section made of a vibration damper. The apparatus may reduce sounds caused between a charger and the photoconductive drum, which charger is of contact electrification system and works to come in contact with the photoconductive drum and thereby charges the same.
However, the image forming apparatus must have the vibration absorption section in the cleaning member, has complex configuration of the cleaning member, requires complex procedures for preparing the cleaning member and thus invites high production cost.
Image forming apparatuses to be placed in the vicinity of users and photoconductors used therein must be miniaturized and slimed down. When down-sized photoconductors having a small outer diameter and being held by a down-sized support are used in image forming apparatuses for the size and weight reduction, the image forming apparatuses often have a small heat capacity. Thus, the photoconductor and cleaning blade often have elevated temperatures. The image forming apparatuses having such miniaturized photoconductors often produce loud fluttering or chattering sounds at early stages of image formation. When the photoconductor has a large length, it often induces irregular rotation and thus induces irregular friction with the cleaning blade, thus inviting louder fluttering or chattering sounds.
In addition, demands have been made to simplify or omit various devices conventionally used in image forming apparatuses for lower cost thereof.
Examples of other conventional techniques for noise reduction in image forming apparatuses are shown below.
JP-A No. 2002-244521 (paragraphs [0005] and [0006]) discloses an image forming method and apparatus. The method includes the steps of forming a latent electrostatic image on an organic photoconductor, developing the latent electrostatic image by a developer containing a toner to form a visible toner image, transferring the visible toner image from the organic photoconductor to an image transfer member, and removing a residual toner on the organic photoconductor using a cleaning device, in which the organic photoconductor has a siloxane resin layer as a surface layer, the cleaning device includes a cleaning blade and a supporting member for the cleaning blade, the supporting member is partially bonded to the cleaning blade in parallel, and the cleaning blade is bonded to a vibration damper. The method and apparatus are intended to maintain good cleaning ability over a long period of time and to produce satisfactory electrophotographic images without image defects.
However, the cleaning blade has increased rigidity due to the bonded vibration damper, thus producing increased chattering sounds.
JP-A No. 05-188833 (paragraphs [0003] and [0006]) discloses a cleaning device for image forming apparatus, comprising a blade for coming in intimate contact with a photoconductor and cleaning residues on the photoconductor, a blade holder for holding the blade, and a holder bracket for holding the blade holder, in which the blade holder or holder bracket has a magnet. The cleaning device is intended to provide an image forming apparatus that avoids reduction in the rigidity of the holder bracket, changes of the intimate contact between the cleaning blade and the photoconductor, and extra vibration of the image forming apparatus.
However, it is impossible to bring the magnet into completely intimate contact with the holder bracket, and small vibration occurs at the contact area between the two members.
JP-A No. 2001-235971 (paragraphs [0008], [0012] and [0014]) discloses a photoconductive drum to be housed in a process cartridge of an image forming apparatus, which comprises a drum cylinder and a vibration damper arranged in the drum cylinder, the vibration damper includes a metallic cylindrical member, an elastic material covering at least part of the outer surface of the cylindrical member, and a coating layer covering the elastic material in intimate contact with the outer surface of the cylindrical member. The vibration damper is intended to absorb the vibration of the photoconductive drum occurring upon the rotation of the photoconductive drum and to increase the adhesion between the vibration damper and the photoconductive drum to thereby reduce noise.
However, the noise cannot be completely prevented and loud noise often occurs when the vibration damper is placed inside the photoconductor.
JP-A No. 2002-116661 (paragraphs [0005] to [0015]) discloses an electrophotographic photoconductor comprising a conductive cylindrical support having an outer diameter of 50 mm or less, a photoconductive layer arranged on the support, and a vibration damper arranged inside the cylindrical support, in which the electrophotographic photoconductor has a cylindricity of 0.03 mm or less. The electrophotographic photoconductor is intended to reduce vibration sounds occurring in contact charging system and vibration sounds of the cleaning blade and to thereby produce high-quality images without irregularity.
The photoconductor is effective to reduce the noise in charging using an alternating voltage, because substantially uniform vibration occurs in the entire photoconductor. However, the friction between the photoconductor and the cleaning blade not always occurs uniformly in the entire photoconductor, and the vibration of the photoconductor in the image forming apparatus often becomes much larger than the level measured in terms of the cylindricity, and the noise is not effectively reduced.
International Publication No. WO 00/49466 discloses an image forming apparatus, in which a silencer formed of pellets for molding a vibration-damping resin containing a base resin, an active component for increasing the dipole moment of the base resin, and an inorganic filler is applied to the inner or outer periphery surface of a photosensitive drum of an image forming apparatus. The vibration of the photoconductive drum is damped and eliminated, realizing high-quality image and low noise.
However, the image forming apparatus does not so effectively work against noise at relatively low frequency, such as one caused by the friction between the vibrating photoconductive drum and the cleaning blade, although it effectively reduces noise produced in contact charging using alternating voltage of several kilohertz.
JP-A No. 10-161426 discloses an image forming apparatus, in which a toner is supplied to a photoconductor at a low rotation of the photoconductor immediately before stop. Noise caused by the friction between the photoconductor and the cleaning blade occurs at a low rotation rate of the photoconductor immediately before stop. Thus, by supplying the toner at this time, the friction between the photoconductor and the cleaning blade is reduced to thereby reduce the noise.
However, the image forming apparatus requires such an extra toner feeding mechanism, which invites higher cost.
JP-A No. 2001-265039 discloses an electrophotographic photoconductor comprising a protective layer made of a curable resin having a torque T50 and a torque T40 with respect to a urethane cleaning blade at a surface temperature of 50° C. and 40° C., respectively, wherein the torque ratio Tr of the torque T50 to the torque T40 is 1.0 to 2.0. This technique is intended to avoid cleaning failure and scratch of the photoconductor.
However, this technique fails to teach effects on the vibration sounds of the cleaning blade, although it is effective to avoid cleaning failure and scratch of the photoconductor.
Another possible solution to reduce the noise is arrangement of a braking mechanism for stopping a photoconductor after image formation to shorten the time period of rotation of the photoconductor at low rate. Thus, the time period of the noise occurrence is shortened, and users may not notice the noise. However, the braking mechanism (control mechanism) is high in cost, because the rotation speed of such photoconductors becomes higher and higher for high-speed image formation, thus the resulting image forming apparatus becomes high in cost.
The noise caused by the increased friction between a photoconductor and a cleaning blade upon stop of the photoconductor occurs after the completion of image formation. Thus, the noise can be avoided by releasing the contact between the photoconductor and the cleaning bade immediately after the completion of image formation. However, such a mechanism for releasing the contact between the photoconductor and the cleaning blade after image formation invites upsizing and higher cost of the image forming apparatus.
If the temperature in the vicinity of the cleaning blade is reduced, the noise caused by the friction between the photoconductor and the cleaning blade can be inhibited. However, such a mechanism for reducing the temperature in the image forming apparatus is adverse to downsizing of the image forming apparatus.
A regular image forming apparatuses comprises a photoconductor and a charger for charging the photoconductor. When the distance between the photoconductor and the charger is short, the image forming apparatus can be miniaturized and reduces ozone and NOx formation in the apparatus. However, the ozone and NOx once formed often build up in such a narrow space between the photoconductor and the charger. The ozone and NOx are oxidative, deteriorate the photoconductive layer of the photoconductor and lead to lower resolution and blur of images.
To avoid the migration of the ozone and NOx formed in a space between the charger and the photoconductor to thereby avoid deterioration of the photoconductive layer, a substance selected from biphenyl compounds and compounds represented by following Formula (I) is incorporated into a photoconductive layer (JP-A No. 09-265194):
wherein R1 is a lower alkyl group; R2 and R3 are the same as or different from each other and are each a substituted or unsubstituted methylene or ethylene group; Ar1 and Ar2 are the same as or different from each other and are each a substituted or unsubstituted aryl group; 1 is an integer of 0 to 4; m is an integer of 0 to 2; and n is an integer of 0 to 2, wherein l, m and n satisfy the following conditions: m+n≧2, and l+m+n≦6, and wherein unsubstituted positions in the benzene ring are hydrogen atoms.
However, the incorporation of a substance selected from the biphenyl compounds and compounds of Formula (I) into the photoconductive layer induces increased noise caused by the friction between the photoconductor and the cleaning blade.